Field of the Invention
This invention relates to aircraft gas turbine engine active clearance control system thermal air distribution systems and, more particularly, panels and manifolds incorporating such panels to spray air on a casing of the engine.
Discussion of the Background Art
Engine performance parameters such as thrust, specific fuel consumption (SFC), and exhaust gas temperature (EGT) margin are strongly dependent upon clearances between turbine blade tips and static seals or shrouds surrounding the blade tips. Active clearance control is a well-known method to modulate a flow of cool or relatively hot air from the engine fan and/or compressor and spray it on high and low pressure turbine casings to shrink the casings relative to the high and low pressure turbine blade tips under steady state, high altitude cruise conditions. The air may be flowed to or sprayed on other static structures used to support the shrouds or seals around the blade tips such as flanges or pseudo-flanges.
One type of active clearance control system includes a thermal air distribution manifold encircling a portion of the outer casing. The manifold includes a circular array of panels and an annular supply tube is connected in fluid supply relationship to plenums of headers of the panels. Cooling air channels of the panel are attached to and in fluid connection with the header. The panels encircle the casing and the channels form continuous spray tubes or rings for spraying cooling air on casing. Examples of manifolds are disclosed in U.S. Pat. No. 7,597,537 to Bucaro, et al., issued Oct. 6, 2009, entitled “Thermal control of gas turbine engine rings for active clearance control” and United States Patent Application No. 20140030066 to Schimmels et al., published Jan. 30, 2014, entitled “ACTIVE CLEARANCE CONTROL MANIFOLD SYSTEM”. U.S. Pat. No. 7,597,537 and United States Patent Application No. 20140030066 are assigned to the General Electric Company, the same assignee as the assignee of this patent and are hereby incorporated herein by reference.
The manifolds are typically mounted to the turbine casing using panel brackets rigidly mounted to casing brackets which, in turn, are rigidly mounted to the turbine casing. This arrangement results in many parts, added weight, and adds to the cost of engine maintenance. Furthermore, the manifold is subject to vibratory stresses causing high cycle fatigue and thermally induced low cycle fatigue which subjects the casing and the manifold assembly to reduced part damage tolerance.